This invention relates to an improved postemulsifiable dye penetrant system and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects, and more particularly to an improved system and method as described above employing therein certain combinations of biodegradable nonionic dye penetrants and biodegradable nonionic emulsifiers. The invention is especially concerned with a postemulsifiable dye penetrant inspection system and method employing stable and sensitive dye penetrant compositions of the above type having the characteristics of being able to disclose a wide range of defective conditions in parts, employing as solvent or vehicle essentially a biodegradable nonionic surfactant in the form of certain combinations or mixtures of certain oxyalkylated alcohols, and also employing emulsifiers for such dye penetrant compositions, containing a biodegradable nonionic surfactant of the general type employed in the dye penetrant, but having a higher degree of water washability, to permit rapid removal of the emulsified dye penetrant by application of water.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high sensitivity.
Volatile type solvents are commonly employed for extending or thinning dye penetrant inspection solutions or compositions. This is done chiefly for the purpose of lowering the viscosity of the penetrant in order to adapt it for application in spraying systems. Thus for example solvents such as kerosene, light fuel oils, and methyl ethyl ketone, all highly volatile solvents, have heretofore been employed in prior art dye penetrants. See for example U.S. Pat. No. 2,806,959. Further, most dye penetrant solutions in practice generally require the use of a combination of solvents, including primary and secondary solvents, extender solvents and wetting agents.
However, the use of volatile solvents in dye penetrant compositions has certain disadvantages. Thus, the use of volatile solvents in dye penetrants results in the evolution of fumes and solvent vapors which are rapidly formed by the evaporating solvent.
Since the use of organic solvents as noted above in the dye penetrant composition does not render the excess dye penetrant composition readily removable from the surface of the part by water, an emulsifier is often applied over the dye penetrant applied to the surface of the part, to render the emulsified excess dye penetrant water washable, followed by removal of the emulsified penetrant with a water wash.
In these dye penetrant systems an additional criterion has recently been developed with respect to both the dye penetrant solutions and emulsifiers. Generally dye penetrant solutions and emulsifiers presently employed and containing solvents and wetting agents present a disposal problem in that they generally contain petroleum solvents and oils which are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria and sewage disposal plants, and constitute serious polluters. Hence the necessity for the development of dye penetrant solutions and emulsifiers for use in a postemulsifiable dye penetrant inspection system, which penetrant solutions and emulsifiers employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, and which render the emulsified penetrant readily water washable, has attained considerable importance.
U.S. Pat. No. 3,716,492 discloses a liquid penetrant composition consisting essentially of a major amount of methyl ester of a fatty acid, such as Methyl Sperm, and which is essentially water insoluble, and a minor amount of a nonionic surfactant such as polyethoxylates of secondary linear alcohols, the methyl ester being the principal liquid vehicle and the nonionic surfactant functioning to emulsify the methyl ester to form a water base emulsion, the methyl ester and nonionic surfactant being biodegradable.
In my above copending applications there are disclosed novel dye penetrant compositions having improved sensitivity characteristics, and which are biodegradable, containing as the sole vehicle for the dye, certain biodegradable nonionic oxyalkylated alcohols. Although dye penetrants of this type have been tested extensively and have proved highly satisfactory and effective for most applications, certain of these formulations having high sensitivity, and containing certain of the above noted oxyalkylated alcohols as surfactant, require employment of relatively high volumes of water and increased pressure to wash excess penetrant from the surface of the test specimen.
Accordingly, an object of the present invention is the provision of a postemulsifiable dye penetrant inspection system and method employing dye penetrant solutions or compositions of the type noted above and described in my above copending applications, and employing certain types of the oxyalkylated alcohols described therein as surfactant, such dye penetrant compositions being biodegradable and having high sensitivity, in conjunction with a postemulsifier which when applied to the dye penetrant, permits ready washability of the emulsified dye penetrant with a reduced volume of water and at reduced pressure as compared to that which would ordinarily be required for removing such dye penetrant composition in the absence of the emulsifier. A particular object of the invention is to provide a postemulsifiable dye penetrant inspection system and method of the above noted type, and which employs as a sole liquid carrier or vehicle for the dye penetrant and as emulsifier, readily available and biodegradable nonionic surfactants of the type disclosed in my above copending applications, and which particularly render the emulsified dye penetrant easily removable employing modest volumes of water at normal washing pressures.